This invention relates to a driving power transmitting apparatus to screws of a twin shaft extruder for extruding plastic and the like, and more particularly to an improved apparatus capable of simplifying a gear transmission system with no accompanying decrease in the driving power.
In the prior art power transmitting apparatus for rotating the screws of a twin shaft extruder, since the two screws are arranged closely adjacent there has been a limit on the diameter of a gear coupled to the screws. It has been impossible to use a large diameter gear coupled to at least one of the screws.
Since these screws have been designed to generate a large torque by using a large input and a small number of rotations, a gear transmission system as shown in FIGS. 6 and 7 of the accompanying drawings has been used.
In the prior art gear transmission system shown in FIGS. 6 and 7, a first screw 11 is driven by a motor 13 via an input shaft 14 and gears 15 and 16 having relatively large diameters. Since it is impossible to make large the diameter of a gear 17 coupled of a second screw 12, as shown in FIG. 7, gears 17 and 18 (these gears constituting a pair) are provided, and the gear 18 is driven by the gear 15 through a gear 19 and a shaft 20, and between paired gears 17 and 18 are interposed in parallel two sets of gear transmission systems comprising two first idle gears 21 and 22, two idle shafts 23 and 24 and two second idle gears 25 and 26 so as to transmit the transmission torque by dividing it into two halves, thereby transmitting a desired torque under a decrease load acting upon respective teeth of gear 17 as disclosed in the Japanese Laid Open Patent Specification No. 62039/1987.
The prior art apparatus described above comprises paired gears 17 and 18, a gear transmission system including two sets of gear transmission systems (21, 23, 25), (22, 24, 26) provided in parallel between the paired gears 17 and 18 and gears 15, 16 and 19 and shaft 20 so that not only the construction of the apparatus becomes complicated but also the length in the longitudinal direction of the screws becomes large.